1. Field of the Invention
Embodiments of the present invention relate to a mobile communication system, and especially to an inter-cell interference coordination method and base station.
2. Description of the Prior Art
The future wireless communication system will adopt OFDM (Orthogonal Frequency Division Multiple Access) technology or single carrier technology as multiple access mode so as to improve the frequency spectrum efficiency. In the uplink, the adoption of the above technologies will make uplink inter-cell interference have the characteristics of non-white noise and fluctuating with the resource allocation and user scheduling. Therefore, in the above system, a method for coordinative resource allocation and user scheduling between neighboring cells is needed so as to reduce the inter-cell interference impact.
Therefore, an OI (Overload Indication) message at X2 interface is defined in the LTE (Long Term Evolution) standardization work to exchange the interference information between neighboring cells and to assist the resource allocation and user scheduling between cells.
The interference control based on OI message is an afterward processing mechanism and its processing procedure is shown in FIG. 1, which includes the following steps.
In step 11, the first base station measures the IOT (Interference over thermal noise) from other interfering cells in the uplink direction.
In step 12, the first base station judges whether the IOT measurement value is larger than the preset threshold value and if yes, proceeds to step 13; otherwise, returns to step 11.
In step 13, the first base station sends the OI message to the second base station to which the neighboring cell belongs via the X2 interface.
In step 14, the second base station which has received the OI message judges whether the user in the cell belonging to the second base station is the main factor causing the high inter-cell interference and if yes, proceeds to step 15; otherwise, no processing will be taken (not shown in FIG. 1).
In step 15, the second base station reduces the transmitting power of the user in the cell belonging to the second base station causing the inter-cell interference high or schedules the user to other subcarriers.
In the OI message, the interference on each subcarrier block is represented by two bits and three levels.
The neighboring cells may exchange information of interference and user scheduling through the OI message so as to reduce the inter-cell interference. However, the related art has the following disadvantages.
The overhead of the interference control method based on the OI message is very large. Since the user who causes the interference to the cell of the first base station exceed the preset threshold value may be in any cell neighboring to the cell of the first base station, the OI message should be sent to each neighboring cell to find the source of the interference.
In the case of 10 MHz bandwidth and 50 subcarrier resource blocks, the first base station needs to send all together 600-bit (50*2*6) OI message overhead to the neighboring 6 cells, i.e. 12-bit message overhead for any one of the subcarrier resource blocks.